The Healthy People 2010 initiative encourages people to engage in regular exercise throughout their lives. Running is one of the most popular fitness activities that Americans engage in. However, due to its repetitive nature, overuse injuries are common. Stress fractures are among the most serious overuse injuries a runner sustains. Retrospective and prospective studies have shown stress fractures are related, in part, to the amount of tibial shock a runner experiences. This suggests that reducing tibial shock would reduce the risk of these serious bony injuries. Therefore, the purposes of this investigation are: 1. to establish whether tibial shock (and consequently vertical loads) can be reduced through realtime feedback in runners exhibiting high shock;2. determine which kinematic strategies are used to reduce lower extremity loading;3. determine whether the changes made during the retraining on the treadmill transfer to overground running;and 4. determine whether these gait changes persist over a 6 month period. 40 male and female runners free of current injuries, aged 18-45 yrs and running at least 10 miles/week will be recruited. They will exhibit increased tibial shock, determined by a prescreening assessment. Subjects will be randomly assigned to one of two groups and undergo a baseline instrumented gait analysis of their lower extremity kinematics and kinetics. 20 subjects will be placed into a 2-week, four times a week retraining program. They will run on an instrumented treadmill with an accelerometer tightly fixed to their distal-medial tibia. With each foot strike, they will be provided with real-time visual feedback of their tibial shock. They will be asked to reduce their shock to within normal limits (indicated by a target on the monitor). Run time will be gradually increased and feedback gradually removed over the 12 sessions. The second group will serve as a control group and undergo a similarly progressed treadmill protocol with no feedback. A post-training overground gait analysis will be conducted following the treatment, and at a 6-month follow-up for both groups. RELEVANCE;Results from this investigation will provide information regarding the ability to alter and maintain gait mechanics to reduce the risk for lower extremity stress fractures. These results can be applied to both preventative medicine as well as rehabilitation with the planned development of a simple portable tool to identify and retrain those at risk.